[PATCH v8 23/27] x86/cet/shstk: ELF header parsing of Shadow Stack

[Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>]

Look in .note.gnu.property of an ELF file and check if Shadow Stack needs
to be enabled for the task.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
---
 arch/x86/Kconfig             |  2 ++
 arch/x86/include/asm/elf.h   | 13 +++++++++++++
 arch/x86/kernel/process_64.c | 34 ++++++++++++++++++++++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index eaf86ef13348..7d13ba326962 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1947,6 +1947,8 @@ config X86_INTEL_SHADOW_STACK_USER
 	select ARCH_USES_HIGH_VMA_FLAGS
 	select X86_INTEL_CET
 	select ARCH_HAS_SHSTK
+	select ARCH_USE_GNU_PROPERTY
+	select ARCH_BINFMT_ELF_STATE
 	---help---
 	  Shadow stack provides hardware protection against program stack
 	  corruption.  Only when all the following are true will an application
diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index 69c0f892e310..fac79b621e0a 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -367,6 +367,19 @@ extern int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
 					      int uses_interp);
 #define compat_arch_setup_additional_pages compat_arch_setup_additional_pages
 
+#ifdef CONFIG_ARCH_BINFMT_ELF_STATE
+struct arch_elf_state {
+	unsigned int gnu_property;
+};
+
+#define INIT_ARCH_ELF_STATE {	\
+	.gnu_property = 0,	\
+}
+
+#define arch_elf_pt_proc(ehdr, phdr, elf, interp, state) (0)
+#define arch_check_elf(ehdr, interp, interp_ehdr, state) (0)
+#endif
+
 /* Do not change the values. See get_align_mask() */
 enum align_flags {
 	ALIGN_VA_32	= BIT(0),
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index af64519b2695..1232f7a6c023 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -818,3 +818,37 @@ unsigned long KSTK_ESP(struct task_struct *task)
 {
 	return task_pt_regs(task)->sp;
 }
+
+#ifdef CONFIG_ARCH_USE_GNU_PROPERTY
+int arch_parse_property(void *ehdr, void *phdr, struct file *f, bool inter,
+			struct arch_elf_state *state)
+{
+	int r = 0;
+	unsigned int property = 0;
+
+	r = get_gnu_property(ehdr, phdr, f, GNU_PROPERTY_X86_FEATURE_1_AND,
+			     &property);
+
+	if (r)
+		return r;
+
+	state->gnu_property = property;
+	return 0;
+}
+
+int arch_setup_property(struct arch_elf_state *state)
+{
+	int r = 0;
+
+	memset(&current->thread.cet, 0, sizeof(struct cet_status));
+
+	if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+		if (state->gnu_property & GNU_PROPERTY_X86_FEATURE_1_SHSTK)
+			r = cet_setup_shstk();
+		if (r < 0)
+			return r;
+	}
+
+	return r;
+}
+#endif
-- 
2.17.1